206 



XVI. THE STEM APEX. 



be done with the aid of a simple or preparation microscope a 

 very useful adjunct to the compound microscope, especially in the 

 preparation of permanent slides. We figure three such simple 

 microscopes, but their number is legion, and form as various as 

 that of the compound microscope itself. An exceedingly simple 

 dissecting stand by Leitz is illustrated in Fig. 79. It has a milk- 

 glass plate as background for the micro-preparation, and an arm 

 to carry lenses. The stand alone costs five marks (shillings). 

 Various lenses can be obtained, ranging from one magnifying 8 

 diameters and having a working distance of 1 inch, to one magnify- 

 ing 40 diameters and with a working distance of J inch, at ten 

 marks each. Fig. 80 represents a very simple dissecting micro- 

 scope by Zeiss, over the stage (ot) of which is placed a lens (d), 



FIG. 79. Simple dissecting stand by Leitz. 



borne on a horizontal arm. The horizontal arm is fixed to a 

 steel upright (st\ which can be moved up and down inside a tube. 

 By this movement the coarse adjustment is brought about. The 

 fine adjustment is effected on the other hand by turning the screw 

 (sr). The instrument is screwed into a dissecting foot, the high 

 ends of which (p) serves as resting places for the hands in the 

 processes of preparation or dissection. The instrument is pro- 

 vided with two, or with three lenses, magnifying 15, 30 and 60 

 diameters, and it is an advantage also to have lenses magnifying 

 five and ten fold. 



The larger dissecting microscope of Zeiss (old form) has also a 

 system of lenses (I, Fig. 81), consisting of three achromatic lenses 

 which can be combined into an objective (06), a tube, and an 

 achromatic eye-piece. In order to work with slighter magnifica- 



